mtd: rawnand: diskonchip: Marking unused variables as __always_unused

'dummy' is never checked (as per the nomenclature) and the use of
'emtpymatch' is currently #if 0'ed out.  We could also #if 0 the
declaration, but #ifery is pretty ugly, so I like to keep it to a
minimum.

Fixes the following W=1 kernel build warning(s):

 drivers/mtd/nand/raw/diskonchip.c: In function ‘DoC_Delay’:
 drivers/mtd/nand/raw/diskonchip.c:219:16: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
 drivers/mtd/nand/raw/diskonchip.c: In function ‘doc200x_calculate_ecc’:
 drivers/mtd/nand/raw/diskonchip.c:706:6: warning: variable ‘emptymatch’ set but not used [-Wunused-but-set-variable]

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Dan Brown <dan_brown@ieee.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201109182206.3037326-16-lee.jones@linaro.org

drivers/mtd/nand/raw/diskonchip.c

@@ -216,7 +216,7 @@ static int doc_ecc_decode(struct rs_control *rs, uint8_t *data, uint8_t *ecc)
 
 static void DoC_Delay(struct doc_priv *doc, unsigned short cycles)
 {
-	volatile char dummy;
+	volatile char __always_unused dummy;
 	int i;
 
 	for (i = 0; i < cycles; i++) {
@@ -703,7 +703,7 @@ static int doc200x_calculate_ecc(struct nand_chip *this, const u_char *dat,
 	struct doc_priv *doc = nand_get_controller_data(this);
 	void __iomem *docptr = doc->virtadr;
 	int i;
-	int emptymatch = 1;
+	int __always_unused emptymatch = 1;
 
 	/* flush the pipeline */
 	if (DoC_is_2000(doc)) {